Electron tube apparatus



Feb. 24, 1959 G. R. CHAMBERS ELECTRON TUBE APPARATUS Filed Fe 27, 1956 United States Patent O ELECTRON TUBE APPARATUS George R. Chambers, San Mateo, Calif., assignor to Eitel-McCullough, Inc., San Bruno, Calif., a corporation of lCalifornia Application February 27, 1956, Serial No. 567,957

3 Claims. (Cl. S15-5.46)

This invention relates to electron tubes and more particularly improved means for tuning tubes, such as klystrons, which are equipped with cavity resonators.

It is well known in the art that the frequency of a cavity resonator can be varied by changing the volume of the i cavity. Further, in the patent to Norton et al., No.

2,619,611, it has been disclosed that a cavity resonator ing its volume `can be located entirely in the external portion, thereby avoiding the complicated sealing arrange ment which is required in order to vary the volume of an evacuated chamber. y

In cavity resonators of the type used in klystrons the dielectric section of the evacuated portion is normally formed in the shape of a cylinder and the external cavity portion is formed in the shape of a split rectangular box fitted symmetrically around the dielectric cylinder. In prior disclosures such as the Norton et al. Patent, No. 2,619,611, the rectangular box is provided at each end with a ilat partition, or tuning door, which is movable toward and away'from the dielectric cylinder to adjust the volume of the cavity resonator.

An object of the present invention is to provide improved tunable cavity resonator structure capable of producing a higher resonant frequency for a given size cavity than was heretofore possible.

Another object of the present invention is to provide improved c avity resonator structure resulting in a greater frequency rangev for a given size cavity than was heretofore possible. Stated in another way, the object is to provide a cavity resonator structure capable of a given frequency range with a smaller size cavity than was heretofore required for said given range.

The present invention involves the use of a tuning door having a concave inner surface which will moreclosely match the convex outer surface of the insulating cylinder than does a conventional llat door. In order to provide the required sliding electrical contact between the door and the walls of the cavity, a ring of contact ngers is disposed around the periphery of the door.

A further object of the invention is to provide a simple arrangement of the contact fingers on a curved tuning door, and further, an arrangement which has a beneficial effect in providing a wide tuning range.

Another object of the invention. is to provide a concave tuning door structure which is usable with a cavity resonator having a radio-frequency coupling loop disposed in the external portionpof the cavity resonator.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of theinvention.

The advantage ofl this composite type of cavity is that the means for adjust- 2,375,369 Patented Feb. 24, 1959 It is to be understood that the invention is not limited to the disclosed species, as variant embodiments thereof are contemplated and may be adopted within the scope of the claims. l

Referring to the drawings:

Figure 1 is an axial sectional view of a 3-cavity klystron incorporating the improved tuning arrangement of the invention. The external portion of the middle cavity is removed to show more clearly the extent of the inner or evacuated portion.

Figure 2 is essentially a side elevational view of the input tuning box taken on the plane of line .2 in Figure l.

Figure 3 isa front elevational view of the tuning box assembled separate from the klystron.

Figure 4 is a sectional view on an enlarged scale taken on the plane of line 4 in Figure 1 and showing one half section of a tuning box in assembled position on the klystron; and,

Figure 5 is an enlarged sectional view of the input coupling taken on the line 5 5 of Figure 3.

Referring in more detail to the drawings, Figure 1 shows `a beam type tube known as a klystron. The tube of spaced tube sections 9, 10, 11 and 12 comprises an elongated evacuated envelope having an electron gun 6 at one end and a collector electrode 7 at the other end. The collector electrode is separated from the electrongun by a drift tube having a plurality forming gaps 13, 14 and 15 therebetween. The drift tube sections are preferably made of copper, and, in order to insulate the collector frointhe drift tube, a ceramic cylinder 16 is employed between the last tube segment 12 and collector 7 which is also preferably made of copper.

Electron gun 6 comprises a cathode 17 housed in a cup-shaped anode 18 preferably made of copper. The anode is connected to the first drift tube segment 9, and electrons from the cathode are focused into the drift tube by a cylindrical focusing electrode 19. The entire gun structure is mounted on a suitable stem 20 which may be of conventional glass, and metal construction with suitable terminals for the various electrodes. Collector electrode-7 at the opposite end of the tube is simply a cupshaped structure which may be provided with suitable exhaust tubulation 22 and cooling structure not shown.

The separate drift tube sections are joined in the following manner to form internal resonator portions 24 adjacent the gaps 13, 14 and 15. The three internal resonator portions are identical, and therefore particular reference is made to the second or intermediate resonator structure which provides the clearest disclosure. Circular end plates 25 of metal such as copper are brazed on the drift tube sections adjacent the gaps 13, 14 and 15. A cylindrical envelope section or window 26 of dielectric material such as ceramic is positioned between the end plates 25 and connected thereto by means of the conventional sealing ange structures 27.

The structure thus far described is conventional and presents a vacuum-tight envelope which forms the tube per se. It will be noted that the cavity resonator portions 24 are not adjustable in size and therefore do not per se provide variable frequency; In order to provide tuning means and increase the volume of the cavity, external cavity resonator portions or tuning boxes 30 are positioned externally of the tube envelope.

InFigure l it will b e noted that no tuning box is shown in connection with the second cavity. This was done to disclose more clearly the appearance of the vacuum enj velope of the tube before the external tuning boxes are of the external tuning boxes is made in two halves. Each half comprises a rectangular box having narrow sides 31 and wide sides 32. In respect to each vinternal cavity portion 24, a tuning box 3b is attached by placing the two halves of the box on diametrically opposite sides of the cavity and clamping the halves together to complete the cavity externally of the vacuum envelope. Any suitable clamping means can be employed to join the two halves of the boxes. For example, the halves can be bolted together, or the quick acting means shown in the drawings can be used. Such means consist of the conventional latches 34 cooperating with the hooks 35, the latches being mounted on opposite box halves from the hooks. l

The physical contact between the tuning box halves and the evacuated portions of cavity resonators24 will now be described. The wide sides 32 of each box half are provided with semi-circular recesses at their inner ends, and a ange 36 is brazed around the rim of each recess. A semi-circular ring 37 is attached to each flange 36 by means of screws 38, and a semi-circular strip of metal forming contact fingers 39 is clamped between flange 36 and ring 37. The size and shape of the semicircular parts is such that when the tuning box halves are clamped together the contact ngers 39 are pressed into good electrical contact with the outer rims of end plates 25 of the evacuated cavities.

lf the tuning boxes 30 formed chambers having fixed volume, they would serve merely to provide cavity resonators which are larger than those formed by the evacuated portions of the cavities. This would provide cavities of larger volume and therefore lower frequency but obviously would not present any means for varying the volume in operation to accomplish tuning. Accordingly, the electrically effective outer ends of the tuning boxes Sti are :made radially adjustable relative to the tube axis. Such electrically effective outer ends are designated generally at 41 and are called tuning doors.

VAs shown best in Figure 4, each of the tuning doors comprises a body portion 42 preferably in the form of a hollow casting to lighten the structure. A particularly important feature of door 41 is that the lower or inner surface of its body portion 42 has a concave shape as will be described in greater detail hereinafter. The internal wall surface of body portion 42 is provided with a plurality of ribs 43 which are tapped to accommodate screws 44. A cover plate 45 is attached by means of screws 44, and two metal strips are clamped between cover plate 4S and the body portion 42 to provide a contact rim comprising inner and outer contact fingers 46 and 4o', respectively. In order to provide means for moving doors 41 in and out along the tuning boxes, a threaded drive shaft 47 is attached to each of the doors. The lower end of each shaft 47 is provided with a flange 48 which rests against the solid center part of body portion 42. A split collar 49 is attached on top of cover plate 45 by means of screws 5t? and extends into a recess on drive shaft 47 which is above flange 48. In this manner the drive shaft is permitted to rotate relative to the tuning door 41 but is not permitted to move axially relative to the door. A plate 51 is mounted in the outer end of each tuning box half by means of screws 52. Plate 51 is thus provided with an apertured center boss 53 which is internally threaded to receive drive shaft 47. Air circulation and lightening holes 54 are preferably provided in plate 51. A knob 56 is rigidly fixed tothe outer end of shaft 47 by means of screw 57. When drive shaft-47 is rotated by means of knob 56, it feeds in and out of threaded boss 53 and thereby moves the tuning door 41 to any desired position.

The tuning door as shown in Figure 4`is positioned approximately at the middle of its travel. The door can be moved outwardly until its outer contact lingers 46' engage plate 51, and it can be moved inwardly to the position shown by dotted line 42. The limit of inward movement is fixed by the fact that when body portion 42 of the door reaches the dotted. line position, knob 56 has moved inwardly into contact with boss 53. It will be seen in Figure 4 that the limit of inward movement is such that the surface of body portion 42 is positioned adjacent the contact finger 39 on the tuning box. If body portion 42 were permitted further inward movement, its lower Contact ngers 46 would tend to become entangled with fingers 39 and would lose contact with the midle portion of walls 32.

It will be understood from Figure 4 that concave shape of tuning doors 41 permits the formation of a smaller cavity resonator than could be obtained if the inner surface of each door were flat. By way of example, it was found that a specific resonant cavity which had a frequency range of 700-925 megacycles with fiat type tuning doors had a range of 7Go-1,00() megacycles when equipped with concave doors as shown in the drawings.

It will be noted that the substitution of the concave door for a flat door increases the high frequency end of the range by seventy-iive megacycles and yet changes the low frequency end by an increase of only six megacycles. It is believed that at least two reasons contribute to this desirable result. Obviously, the door 41 occupies more volume by reason of its concave shape than it would occupy if it were made hat across the bottom edges of contact" fingers 46. However, this additional volume of the concave door is a much higher percentage of the effective resonatorvolume when the door is at its inward limit of movement than when the door is at its outward A second reason why the concave door substantially increases the high frequencyend of the tuning range without appreciable effect on the low frequency end is that the effective inner surface of door 4l is believed to-move outwardly on body portion 42' as thedoor itself is moved I outwardly. In order to explain this phenomenon it is desirable first to point out that there is an air gap between each side of the tuning box and the adjacent side of the body portion 42 of the tuning door.` Figure 4 shows such air gaps between body portion 42 and walls 31 of the tuning box; the same size air gap exists between the body portion and walls 32. As will be understood by those skilled in the art, the electrostatic field within each cavity resonator is concentrated at the center of the cavity and decreases radially outwardly of the center. Thus the eld is strongest within the gaps 13, 14 and 15 and is weakest at the outer ends of tuning boxes 30.'

The capacitance across the gap between the tuning door body and the adjacent tuning box walls is a function of the field strength in which the door is positioned, such capacitance being high in a strong field and low in a weak held. Thus, when the door is in the inward position shown by dotted line 42, very high capacitance exists y between body portion 42 and the tuning box walls. Such high capacitance of course means that radio-frequency current can flow with relative ease from the tuning box walls to the tuning door body 42. As a result the current is shorted almost directly from the tuning box walls to the edges of the inward surface of tuning door body 42, so that the inner surface of body portion 42 forms the outer end of the cavity.

However, when the tuning door is moved to its outward limit, it is positioned in a relatively weak electrostatic iield, and a very low capacitanceexists between body portion 42 and the tuning box walls. The existence of such low capacitance means that the current inds it diicult to Vtlow across the gap between the cavity walls and the tuning door body 42. As a result the current passes from the cavity walls to the tuning door at an clfective position radially outward of the inward surface of body portion 42. Depending on the physical dimensions and electrical values involved, some or all of the current can be shorted across the contact fingers 46 and 46', and the remaining current passes through tbe gap radially outward from the edges of the inner surface of body portion 42. Thus, as the tuning door is moved toward its outer limit, the effective outer end of the cavity tends to become coincident with the rim of contact fingers 46 and 46', and, as the door is moved toward its inner limit, the effective outer end of the cavity tends to become coincident with the inner surface of body portion 42.

Referring again to Figure 4, it will be seen that the shape of the inner surface of door 41 which will result in the smallest possible resonant cavity is a shape such that when the door is in its inward position the concave portion of each door completely surrounds its half of the insulating cylinder 26 and is concentric therewith. The center portion of the door shown in Figure 4 is shaped in this manner and forms a segment of a circle having a radius such that when the door is in the inward or dotted position said circle is concentric with the cylinder 26. The reason why the outer portions of the concave door surface shown in Figure 4 depart from the optimum circular shape is to avoid damaging contact with the coupling member 60 which carries radio-frequency energy into the .first or input resonant cavity. A similar coupling arrangement is of course required to extract radio-frequency energy from the third or output cavity.

The energy coupling member 60 is shown in detail in Figure 5 and comprises coaxial conductors 61 and 62 separated by an insulating sleeve 63. A coupling loop 64 is connected between the conductors 61 and 62 internally of the cavity resonator. As shown in Figures 3 and 4, the coupling member 60 is preferably located in the side 31 of tuning box 30 in such a way that the loop 64 is positioned between dielectric cylinder 26 and wall 31. Since it is necessary to adjust the orientation of loop 64 for optimum performance, the outer conductor is rotatably received in wall 31. In order to secure the loop in any selected position, a collar 65 is fitted over a circular flange on conductor 61 and clamped in place by screws 66. In Figures 4 and 5 the loop 64 is shown rotated parallel to walls 32. This is the critical position of the loop relative to tuning door 41, and the door is shaped to avoid contact with the loop in this position.

In the light of the preceding description it will be understood that the cavity resonator for each of the gaps 13, 14 and 15 comprises a composite structure consisting of an internal resonator portion 24 and an external portion 30. As previously described, a split box type of construction is preferred for the external portion of the cavity. However, it should be understood that the advantages of the concave tuning door would be equally effective if the external resonator'portion 30 were permanently attached to the tube. For example, the external portion could be formed by extending the end plates 25 to replace the wide tuning box walls 32, and the narrow walls 31 could be replaced by long plates brazed between the extended end plates 2S.

Having thus described the invention, `what is claimed as new and desired to be secured by Letters Patent is:

1. A cavity resonator type electron tube apparatus comprising, an electron gun forming one end of an evacuated envelope, a collector electrode forming the other end of said envelope, a drift tube extending between said gun and said collector electrode and forming side wall portions of said evacuated envelope, said drlft tube comprising spaced sections with a gap therebetween, a composite cavity resonator disposed transversely of said drift tube axis adjacent said gap and having an inner evacuated portion and an outer portion, said resonator comprising metal walls extending outwardly from said drift tube sections and a cylinder of dielectric material sealed between said walls forming a side wall portion of said envelope and providing a vacuunrtight partition between the internal and external portions of the resonator, a tuning door positioned in the external portion of said resonator and movable toward and away from said dielectric cylinder, said tuning door having a concave inner surface facing the convex outer surface of said dielectric cylinder, an energy coupling loop mounted in the wall of said resonator externally of said dielectric cylinder, and means providing an end limit for inward movement of said door, the shape of said concave door surface being such that when the door is moved to said inward end limit the central portion of said concave inner surface is substantially concentric with said dielectric cylinder and the outer portions of said inner surface are spaced from said loop.

2. A composite cavity resonator comprising a vacuumtight internal portion and a portion external thereto, said internal portion comprising a cylindrical wall section of dielectric material, a tuning door in said external portion, said tuning door comprising a planar contact rim in sliding engagement with the inside of said external portion, and a body portion of said door extending from lsaid rim toward said dielectric wall section and spaced from the inside of said external portion, said body portion having a curved surface adjacent said cylindrical wall section adapted to partially surround said wall section.

3. A cavity resonator type electron tube apparatusV comprising an electron gun forming one end of an evacuated envelope, a collector electrode forming the other end of said envelope, a drift tube extending between said gun and said collector electrode and forming side wall portions of said envelope, said drift tube comprising spaced sections with a gap therebetween, a composite cavity resonator disposed transversely of said drift tube axis adjacent said gap and having an inner evacuated portion and an outer portion, said resonator comprising metal walls extending outwardly from said drift tube section and a cylinder of dielectric material sealed between said walls forming a side wall portion of said envelope and providing a vacuum-tight partition between the internal and external portions of the resonator, a tuning door positioned in the external portion of said resonator and movable toward and away from said dielectric cylinder, said tuning door comprising a body portion having a concave surface facing the convex outer surface of said dielectric cylinder and a rim of contact fingers disposed about said body portion in a plane spaced from said concave surface, and means providing an end limit for inward movement of said door, the shape of said concave door surface being such that when the door is moved to said inward end limit the central portion of said concave inner surface is substantially con-centric with said dielectric cylinder and the outer portions of said concave surface partially surrounds said dielectric cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 2,410,109 Schelleng Oct. 29, 1946 2,468,655 Cole et al. Apr. 26, 1949 2,619,611 Norton et al Nov. 25, 1952 2,629,066 Eitel et al Feb. 17, 1953 2,779,895 Doolittle Jan. 29, 1957 

